In high-voltage battery packs of new energy automobiles and energy storage systems, effective balancing must be performed among individual batteries connected in series in the high-voltage battery packs in order to ensure that the battery system has sufficient charging and discharging energy and to prolong the service life of the battery packs. Most of the balancing technologies currently available achieve the passive discharging balance by means of discharging via a resistor. This is a kind of unidirectional energy-consuming balancing approach, which has a small balancing current (this has a high requirement on consistency among the individual batteries themselves) and causes heat generation.
Currently, bidirectional isolated DC-DC converter apparatuses are mainly used in solar energy storage control systems, and motor driving and energy feedback systems of electromobiles, and most of them adopt a single-chip microcontroller or a digital signal processor (DSP) for perform the control and adopt a transformer for perform the isolated voltage-transformation so as to achieve the bidirectional energy transferring.
China Patent CN201120283402.9 discloses a bidirectional DC-DC converter, which comprises a current detecting circuit, a voltage detecting circuit, a controller module, a pulse width modulating circuit and a high-frequency dual-ratio transformer, and is applicable to systems in which the charging and discharging DC/DC voltages which are varied greatly. However, the circuit of this kind of DC-DC converter adopts high turn ratios and suspended windings, and it leads to a large leakage inductance and parasitic parameters, which tends to cause electromagnetic compatibility problems. Furthermore, the aforesaid bidirectional DC-DC converter adopts multi-path change-over switches, which make both the structure and the control complex.
China Patent CN201210488856.9 discloses a bidirectional DC-DC converter, which comprises a power-converting unit, an input-voltage sampling unit, an output-voltage sampling unit, a current sampling and processing unit, a PWM controlling unit and a function controlling unit. However, this kind of bidirectional DC-DC converter is only applicable to perform the charging and discharging balance among battery units in a high-voltage battery pack and is only able to achieve a constant current at one side instead of at both sides. Furthermore, when a high turn ratio is needed, a two-step voltage boosting mode must be adopted in the bidirectional DC-DC converter, which tends to introduce the electromagnetic compatibility problems and makes both the structure and the control complex. During the DC-DC converting process, high-frequency signals tend to interfere with the functional controlling unit to affect the reliability of the whole system.
Accordingly, it is necessary to provide a novel bidirectional isolated DC-DC converter to solve the aforesaid problems.